Moisture induced damage is a significant problem on society's transportation infrastructure including roads and bridges. Hot Mix Asphalt (HMA) is commonly used as a construction material on these structures because of its relatively low initial cost and low repair costs over alternate materials. While the HMA is in service on these structures, it is exposed to a variety of weathering elements including moisture. Moisture induced damage can cause large rehabilitation and repair expenses and cause significant inconvenience to the public while roads and structures are closed for repairs.
One failure mechanism that plays a part in the destruction of the HMA material is the degradation of the bond between the asphalt binder and the aggregate materials caused by moisture. This degradation, more commonly referred to as stripping, can cause a variety of problems in the HMA structure. Stripping is the failure of the adhesion between the aggregate and asphalt cement binder in HMA. Stripping occurs when water gets between the asphalt binder and the aggregate surface, and/or when water interacts with the asphalt binder and reduces its cohesive properties. Factors that influence the occurrence and severity of stripping include physical and chemical properties of both the aggregate and asphalt cement and the environment in which the pavement exists. The combination of temperature, water, and the shearing force applied by tires is a likely cause for stripping. It is therefore important to obtain an accurate measure of the resistance to stripping as a critical part of evaluating the HMA concrete material properties. If moisture susceptibility can be detected early in the design phase of the HMA construction cycle, precautions can be taken to reduce the susceptibility to stripping in the field, such as adding chemical anti-stripping agents to the HMA mixture. However, these anti-stripping agents add cost to the mixture, so unnecessary use of such agents is undesirable.
Several tests currently exist for evaluating the susceptibility of the HMA to stripping damage, however, each test has its shortcomings. These shortcomings include inconsistent results, large bulky testing equipment, long testing times, time consuming specimen preparation and conditioning, etc. Most of the strength/modulus type tests available simply look at “conditioned vs. unconditioned”, an approach that may not yield the desired results. Many of the current devices also require specialized specimen preparation equipment and procedures. Some existing reciprocating type material testing machines utilize a crank-arm system to move the load across the specimen and therefore provide a sinusoidal velocity profile rather than a constant velocity loading profile.